Complementary SONOS integration into CMOS flow

ABSTRACT

Methods of integrating complementary SONOS devices into a CMOS process flow are described. The method begins with depositing and patterning a first photoresist mask over a surface of a substrate to expose a N-SONOS region, and implanting a channel for a NSONOS device through a first pad oxide, followed by depositing and patterning a second photoresist mask to expose a P-SONOS region, and implanting a channel for a PSONOS device through a second pad oxide. Next, a number of Nwells are concurrently implanted for the PSONOS device and a PMOS device in a core region of the substrate. Finally, the first and second pad oxides, which were left in place to separate the P-SONOS region and the N-SONOS region from the first and second photoresist masks, are concurrently removed. In one embodiment, implanting the Nwells includes implanting a single, contiguous deep Nwell for the PSONOS and PMOS device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/305,122 filed Jun. 16, 2014, which claims the benefit of priorityunder 35 U.S.C. 119(e) to U.S. Provisional Patent Application Ser. No.61/936,506, filed Feb. 6, 2014, and to U.S. Provisional PatentApplication Ser. No. 61/915,390, filed Dec. 12, 2013 all of which areincorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates generally to semiconductor devices, andmore particularly to memory cells including embedded or integrallyformed silicon-oxide-nitride-oxide-semiconductor (SONOS) devices andmetal-oxide-semiconductor (MOS) devices and methods for fabricating thesame.

BACKGROUND

For many applications, such as system-on-chip (SOC) architecture, it isdesirable to integrate logic devices and interface circuits based uponMOS transistors or devices and silicon-oxide-nitride-oxide-semiconductor(SONOS) transistors or devices, on a single chip or substrate to createnon-volatile memory (NVM). MOS devices are typically fabricated using astandard or baseline complimentary-metal-oxide-semiconductor (CMOS)process flows. SONOS devices include charge-trapping gate stacks inwhich a stored or trapped charge changes a threshold voltage of thenon-volatile memory device to store information as a logic 1 or 0. Theintegration of these dissimilar devices in SOC architecture ischallenging and becomes even more problematic when attempting to formcomplementary N and P-type SONOS devices with CMOS devices on a singlechip or integrated circuit (IC).

SUMMARY

Methods of integrating complementary SONOS devices into a CMOS processflow are described. The method begins with depositing a hardmask (HM)over a substrate including a P-SONOS region and an N-SONOS region. Inseveral embodiments, the substrate further includes a MOS region inwhich a number of MOS devices are to be formed and the HM isconcurrently deposited over the MOS region. A first tunnel mask (TUNM)is formed over the HM exposing a first portion of the HM in the N-SONOSregion. The first portion of the HM is etched, a channel for a N-typeSONOS device implanted through a first pad oxide overlying the N-SONOSregion and the first TUNM removed. A second TUNM is formed exposing asecond portion of the HM in the P-SONOS region. The second portion ofthe HM is etched, a channel for a P-type SONOS device implanted througha second pad oxide overlying the P-SONOS region and the second TUNMremoved. The first and second pad oxides are concurrently etched, andthe HM removed.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will be understood more fully fromthe detailed description that follows and from the accompanying drawingsand the appended claims provided below, where:

FIG. 1 is a flowchart illustrating an embodiment of a method forfabricating a memory cell including complementarysilicon-oxide-nitride-oxide-semiconductor (SONOS) devices and ametal-oxide-semiconductor (MOS) devices;

FIGS. 2A-2S are block diagrams illustrating cross-sectional views of aportion of a memory cell during fabrication of the memory cell accordingto the method of FIG. 1; and

FIG. 3 is a flowchart illustrating another embodiment of a method forfabricating a memory cell including complementary SONOS devices and ametal-oxide-semiconductor (MOS) devices; and

FIGS. 4A-4J are block diagrams illustrating cross-sectional views of aportion of a memory cell during fabrication of the memory cell accordingto the method of FIG. 3; and

FIG. 5 is a block diagram illustrating cross-sectional views of aportion of a memory cell during fabrication of the memory cell accordingto an alternative embodiment of either the method of FIG. 1 or FIG. 3.

DETAILED DESCRIPTION

Embodiments of methods of integrating complimentarysilicon-oxide-nitride-oxide-semiconductor (CSONOS) into a complimentarymetal-oxide-semiconductor (CMOS) fabrication process or process flow toproduce non-volatile memory (NVM) cells are described herein withreference to figures. However, particular embodiments may be practicedwithout one or more of these specific details, or in combination withother known methods, materials, and apparatuses. In the followingdescription, numerous specific details are set forth, such as specificmaterials, dimensions and processes parameters etc. to provide athorough understanding of the present invention. In other instances,well-known semiconductor design and fabrication techniques have not beendescribed in particular detail to avoid unnecessarily obscuring thepresent invention. Reference throughout this specification to “anembodiment” means that a particular feature, structure, material, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention. Thus, the appearances ofthe phrase “in an embodiment” in various places throughout thisspecification are not necessarily referring to the same embodiment ofthe invention. Furthermore, the particular features, structures,materials, or characteristics may be combined in any suitable manner inone or more embodiments.

The terms “over,” “under,” “between,” and “on” as used herein refer to arelative position of one layer with respect to other layers. As such,for example, one layer deposited or disposed over or under another layermay be directly in contact with the other layer or may have one or moreintervening layers. Moreover, one layer deposited or disposed betweenlayers may be directly in contact with the layers or may have one ormore intervening layers. In contrast, a first layer “on” a second layeris in contact with that second layer. Additionally, the relativeposition of one layer with respect to other layers is provided assumingoperations deposit, modify and remove films relative to a startingsubstrate without consideration of the absolute orientation of thesubstrate.

Briefly, in one embodiment the method begins with depositing a hardmask(HM) over a surface of a substrate including a first-SONOS region and asecond-SONOS region in which a pair of complementary SONOS devices areto be formed. A first tunnel mask (TUNM) is formed over the HM exposinga first portion of the HM in the second-SONOS region, the first portionof the HM is etched, and a channel for a first SONOS device implantedthrough a first pad oxide overlying the second-SONOS region after whichthe first TUNM is removed. Next, a second TUNM is formed over the HMexposing a second portion of the HM in the first-SONOS region, thesecond portion of the HM is etched, and a channel for a second SONOSdevice implanted through a second pad oxide overlying the first-SONOSregion after which the second TUNM is removed. Finally, the first andsecond pad oxides in the first-SONOS region and second-SONOS regions areconcurrently etched, and the HM removed. The first and second SONOSregions are or will be doped with opposite types of dopants. Thus,although in the following exemplary embodiments the first-SONOS regionis described as being a P-SONOS region and the second-SONOS region as anN-SONOS region, it will be understood that in other embodiments, thefirst-SONOS region may be an N-SONOS region and the second-SONOS regiona P-SONOS region without departing from the scope of the invention.

The CSONOS devices may include devices or transistors implemented usingSilicon-Oxide-Nitride-Oxide-Silicon (SONOS) orMetal-Oxide-Nitride-Oxide-Silicon (MONOS) technology.

An embodiment of a method for integrating or embedding CSONOS into aCMOS process flow will now be described in detail with reference to FIG.1 and FIGS. 2A through 2S. FIG. 1 is a flowchart illustrating anembodiment of a method or process flow in which a hardmask is depositedover a surface of substrate before tunnel masks (TUNM) are formed forthe CSONOS and SONOS wells and/or channels implanted. FIGS. 2A-2S areblock diagrams illustrating cross-sectional views of a portion of amemory cell 200, including a pair of complementary SONOS devices and apair or a number of MOS devices, two of which are shown, duringfabrication of the memory cell according to the method of FIG. 1. In oneembodiment, the pair of MOS devices is a pair of complementary MOS(CMOS) devices.

Referring to FIG. 1 and FIG. 2A, the process begins with forming anumber of isolation structures 202 in a wafer or substrate 204 (step102). The isolation structures 202 isolate the memory cell being formedfrom memory cells formed in adjoining areas (not shown) of the substrate204 and/or isolate the pair of complementary SONOS devices 206 a-206 bbeing formed in a SONOS region 208 of the substrate from one another,and from a number of MOS devices 210 a-210 b being formed in one or moreadjoining MOS regions 212, only one of which is shown.

It is noted that in the embodiment shown the pair of complementary SONOSdevices include a p-type SONOS device (P-SONOS 206 a) formed in aP-SONOS region 208 a, and a N-type SONOS device (N-SONOS 206 b) formedin a N-SONOS region 208 b. By P-type SONOS device it is meant a devicehaving a channel region doped with a P-type, acceptor dopant such asboron. Similarly, by N-type SONOS device it is meant a device having achannel region doped with an N-type, donor dopant such as phosphorus orarsenic.

It is noted that the number of MOS devices 210 a-210 b can include bothlow-voltage field effect transistors (LV-FET) in a core of anon-volatile memory (NVM) and high-voltage field effect transistors(HV-FET) in an input/output (I/O) circuit of the NVM. For purposes ofexplanation and to simplify the figures the MOS devices 210 a-210 b areshown as including a LV-FET 210 a in the core of the NVM and a HV-FET210 b in the I/O circuit of the NVM. Although not shown in this figure,it will be understood the MOS devices 210 a-210 b can be and generallyare one half of a complementary pairs of CMOS in the core and/or the I/Ocircuit of the NVM, all of which are integrally and concurrently formedalong with the pair of the CSONOS devices.

The isolation structures 202 include a dielectric material, such as anoxide or nitride, and may be formed by any conventional technique,including but not limited to shallow trench isolation (STI) or localoxidation of silicon (LOCOS). The substrate 204 may be a bulk wafercomposed of any single crystal or polycrystalline material suitable forsemiconductor device fabrication, or may include a top epitaxial layerof a suitable material formed on a substrate. Suitable materialsinclude, but are not limited to, silicon, germanium, silicon-germaniumor a III-V compound semiconductor material.

A pad oxide 214 is formed over a surface 216 of the substrate 204 inboth the NVM region 208 and the MOS regions 212. The pad oxide 214 canbe silicon dioxide (SiO₂) having a thickness of from about 10 nanometers(nm) to about 20 nm and can be grown by a thermal oxidation process orin-situ steam generation (ISSG).

Referring again to FIG. 1 and FIG. 2A, dopants are then implanted intosubstrate 204 through the pad oxide 214 to form channels 218 and wells220 for one or more of the MOS devices 210 a-210 b that will be formedin the MOS region 212 (step 104). Generally, this involves severalseparate deposition, lithography, implant and stripping processes toimplant wells and channels for different types of devices, formed indifferent areas, i.e., the core or I/O circuit of the NVM. For example,to perform well and channel implants of a N-type MOS device in the core,core MOS 210 a, a photoresist layer is deposited and patterned usingstandard lithographic techniques to block or shield both the SONOSregion 208 and P-type devices in the MOS region 212, and implanting anappropriate ion species at an appropriate energy to an appropriateconcentration. For example, BF₂ can be implanted at an energy of fromabout 10 to about 100 kilo-electron volts (keV), and a dose of fromabout 1e12 cm⁻² to about 1e14 cm⁻² to form an N-type MOS (NMOS)transistor. A P-type MOS (PMOS) transistor may likewise be formed byimplantation of Arsenic or Phosphorous ions at any suitable dose andenergy. It is to be understood that implantation can be used to formchannels 218, in all of the MOS regions 212 at the same time, or atseparate times using standard lithographic techniques, including apatterned photoresist layer to mask one of the MOS regions. After theimplants have been performed, the patterned resist layer is stripped ineither an ashing process using oxygen plasma, or in a photoresist stripusing a commercially available strip or solvent. Another photoresistlayer is deposited and patterned to block or shield both the SONOSregion 208 and N-type devices in the MOS region 212 prior to performingwell and channel implants of a P-type MOS device in the core. Theprocess is then repeated for the MOS devices in the MOS device in theI/O circuit, I/O MOS 210 b.

Next, referring to FIG. 1 and FIG. 2B a hardmask 222 is deposited overthe surface 216 of the substrate 204 (step 106). Generally, the hardmask222 is formed concurrently over both the P-SONOS region 208 a and theN-SONOS region 208 b. In some embodiments, such as that shown, thehardmask 222 is formed concurrently over substantially the entiresurface 216 of the substrate 204, including both the P-SONOS region 208a and the N-SONOS region 208 b and the MOS region 212.

Generally, the hardmask 222 can include one or more layers of materialthat can be patterned or opened using photoresist and standardlithographic techniques, but which is not itself photosensitive andprotects underlying surface and structures formed therein from thephotoresist and lithographic processes as well as from implants and etchprocess performed through openings formed in the hardmask. Suitablematerials for the hardmask 222 include, for example, a layer of fromabout 5 to about 20 nm of silicon nitride (Si_(x)N_(y)), or siliconoxynitride (SiON) deposited by any known nitride deposition process. Forexample, in one embodiment a nitride hardmask is formed in step 106 in alow pressure chemical vapor deposition (LPCVD) process using a siliconsource, such as silane (SiH₄), dichlorosilane (SiH₂Cl₂),tetrachlorosilane (SiCl₄) or Bis-TertiaryButylAmino Silane (BTBAS), anda nitrogen source, such as NH₃ and N₂O.

Next, referring to FIG. 1 and FIG. 2C a first tunnel mask (TUNM 224) isformed by depositing a photoresist layer on or overlying substantiallyan entire surface of the hardmask 222, patterning the photoresist layerusing standard lithographic techniques (step 108). Because an opening226 in the patterned photoresist layer exposes a first portion of the HM222 in the N-SONOS region 208 b, the first TUNM 224 may also be referredto as the N-TUNM.

Referring to FIG. 1 and FIG. 2D, the first portion of the HM exposedthrough the opening 226 in the first or N-TUNM 224 is etched or removedusing any suitable wet or dry etching technique, depending on thematerial of the hardmask and the underlying structures or layers (step110). For example, in those embodiments in which the hardmask 222includes a layer of silicon nitride overlying a pad oxide 214, thehardmask can be etched using a standard low pressure nitride etch at amoderate power (about 500 W) in a plasma of a fluorine containing gas,such as CF₄, or CHF₃, which exhibits good selectivity to silicon oxides,such as the silicon dioxide (SiO2) of the underlying pad oxide 214and/or the STI 202 structures.

Next, referring again to FIG. 1 and FIG. 2D, dopants of an appropriateenergy and concentration are implanted through the opening in thehardmask 222 and the pad oxide 214 to form a channel 228 for the N-SONOSdevice 206 b, and, optionally, a well (not shown in this figure) inwhich the channel for the N-SONOS device is formed (step 112). In oneembodiment, the well can be implanted with boron ions (BF₂) at an energyof from about 100 to about 500 kilo-electron volts (keV), and a dose offrom about 1E12/cm² to about 5E13/cm² to form a Pwell. The channel 228can be implanted with Arsenic or Phosphorous ions at an energy of fromabout 50 to about 500 kilo-electron volts (keV), and a dose of fromabout 5e11cm⁻² to about 5e12 cm⁻² to form a N-SONOS device 206 b.

Referring to FIG. 1 and FIG. 2E, the first or N-TUNM 224 is removed orstripped in either an ashing process using oxygen plasma, or aphotoresist strip or solvent (step 114).

Next, referring to FIG. 1 and FIG. 2F a second tunnel mask (TUNM 230) isformed by depositing a photoresist layer on or over substantially anentire surface of the hardmask 222 and the surface 216 of the substrate204 exposed by the first hardmask etch step, and patterned usingstandard lithographic techniques (step 116). Because an opening 232 inthe patterned photoresist layer exposes a second portion of the hardmask222 in the P-SONOS region 208 a, the second TUNM 230 may also bereferred to as the P-TUNM. It is noted that the pad oxide 214 isolatesthe surface 216 of the substrate 204 from the photoresist of second TUNM230 in the N-SONOS region 208 b.

Referring to FIG. 1 and FIG. 2G, the second portion of the hardmask 222exposed through the opening 232 in the second or P-TUNM 230 is etched orremoved using any suitable wet or dry etching technique, depending onthe material of the hardmask and the underlying structures or layers(step 118). For example, as described above in connection with N-TUNM224, in those embodiments in which the hardmask 222 includes a layer ofsilicon nitride overlying a pad oxide 214, the hardmask can be etchedusing a standard low pressure nitride etch at a moderate power (about500 W) in a plasma of a fluorine containing gas, such as CF₄, or CHF₃,which exhibits good selectivity to silicon oxides, such as the silicondioxide (SiO2) of the underlying pad oxide 214 and/or the STI 202structures.

Referring again to FIG. 1 and FIG. 2G, dopants of an appropriate energyand concentration are implanted through the opening in the hardmask 222and the pad oxide 214 to form a channel 234 and a well or deep well 236in which the P-SONOS device 206 a is formed (step 120). In oneembodiment, the well can be implanted with Arsenic or Phosphorous at anenergy of from about 200 to about 1000 kilo-electron volts (keV), and adose of from about 1E12/cm²to about 5E13/cm² to form a deep Nwell. Thechannel 234 can be implanted with boron ions (BF₂) at an energy of fromabout 10 to about 100 kilo-electron volts (keV), and a dose of fromabout 1e12cm⁻² to about 1e13 cm⁻² to form a P-SONOS device 206 a.

Referring to FIG. 1 and FIG. 2H, the second or P-TUNM 230 is removed orstripped in either an ashing process using oxygen plasma, or aphotoresist strip or solvent (step 122).

Next, referring to FIG. 1 and FIG. 2I, the pad oxide 214 over both theP-SONOS region 208 a and the N-SONOS region 208 b is concurrentlyremoved in a tunnel mask etch through the openings previously formed inthe hardmask 222 (step 124). The tunnel mask etch can be accomplished,for example, in a wet clean process using a 10:1 buffered oxide etch(BOE) containing a surfactant. Alternatively, the wet clean process canbe performed using a 20:1 BOE wet etch, a 50:1 hydrofluoric (HF) wetetch, a pad etch, or any other similar hydrofluoric-based wet etchingchemistry.

Referring to FIG. 1 and FIG. 2J, the hardmask 222 is substantiallyentirely stripped or removed (step 126). The hardmask 222 can be removedusing the same process and chemistry previously used to form openings inthe hardmask. For example, in embodiments in which the hardmask 222includes a silicon nitride layer, it can be removed using a standard lowpressure nitride etch at a moderate power (about 500 W) in a plasma of afluorine containing gas, such as CF₄, or CHF₃, which exhibits goodselectivity to silicon oxides, such as the silicon dioxide (SiO2) of thepad oxide 214 remaining over the MOS devices 210 a-210 b in the MOSregion 212 and the STI 202 structures, and to the underlying silicon ofthe substrate in the SONOS region 208. Alternatively, the siliconnitride can also be removed by a wet etch using Phosphoric acid (H₃PO₄)at a temperature of about 150° C. to 160° C.

Referring to FIGS. 1 and FIGS. 2K through 2L, a number of dielectric oroxide-nitride-oxide (ONO) layers, shown collectively as dielectriclayers 238 in FIG. 2L, are formed or deposited over the surface 216 ofthe substrate 204, a mask formed on or overlying the dielectric layers,and the dielectric layers etched to form ONO or dielectric stacks 240 ofthe N-SONOS device 206 b and the P-SONOS device 206 a in the N-SONOSregion 208 b and the P-SONOS region 208 a (step 128).

Referring to FIG. 2L, the number of dielectric layers 238 includes atunneling layer 242 overlying the surface 216 of the substrate 204, acharge-trapping layer 244 overlying the tunneling layer and a blockinglayer 246 overlying the charge-trapping layer. The tunneling layer 242may be any material and have any thickness suitable to allow chargecarriers to tunnel into an overlying charge-trapping layer under anapplied gate bias while maintaining a suitable barrier to leakage whenthe SONOS devices (P-SONOS device 206 a and N-SONOS device 206 b) areunbiased. In certain embodiments, tunneling layer 242 is silicondioxide, silicon oxy-nitride, or a combination thereof and can be grownby a thermal oxidation process, using ISSG or radical oxidation.

In one embodiment a silicon dioxide tunneling layer 242 may be thermallygrown in a thermal oxidation process. For example, a layer of silicondioxide may be grown utilizing dry oxidation at 750 degrees centigrade(° C.)-800° C. in an oxygen containing gas or atmosphere, such as oxygen(O₂) gas. The thermal oxidation process is carried out for a durationapproximately in the range of 50 to 150 minutes to effect growth of atunneling layer 242 having a thickness of from about 1.0 nanometers (nm)to about 3.0 nm by oxidation and consumption of the exposed surface ofsubstrate.

In another embodiment a silicon dioxide tunneling layer 242 may be grownin a radical oxidation process involving flowing hydrogen (H₂) andoxygen (O₂) gas into a processing chamber at a ratio to one another ofapproximately 1:1 without an ignition event, such as forming of aplasma, which would otherwise typically be used to pyrolyze the H₂ andO₂ to form steam. Instead, the H₂ and O₂ are permitted to react at atemperature approximately in the range of about 900° C. to about 1000°C. at a pressure approximately in the range of about 0.5 to about 5 Torrto form radicals, such as, an OH radical, an HO₂ radical or an oxygen(O) diradical, at the surface of substrate. The radical oxidationprocess is carried out for a duration approximately in the range ofabout 1 to about 10 minutes to effect growth of a tunneling layer 242having a thickness of from about 1.0 nanometers (nm) to about 4.0 nm byoxidation and consumption of the exposed surface of substrate. It willbe understood that in this and in subsequent figures the thickness oftunneling layer 242 is exaggerated relative to the pad oxide 214, whichis approximately 7 times thicker, for the purposes of clarity. Atunneling layer 242 grown in a radical oxidation process is both denserand is composed of substantially fewer hydrogen atoms/cm³ than atunneling layer formed by wet oxidation techniques, even at a reducedthickness. In certain embodiments, the radical oxidation process iscarried out in a batch-processing chamber or furnace capable ofprocessing multiple substrates to provide a high quality tunneling layer242 without impacting the throughput (wafers/hr.) requirements that afabrication facility may require.

In another embodiment, tunneling layer 242 is deposited by chemicalvapor deposition (CVD) or atomic layer deposition and is composed of adielectric layer which may include, but is not limited to silicondioxide, silicon oxy-nitride, silicon nitride, aluminum oxide, hafniumoxide, zirconium oxide, hafnium silicate, zirconium silicate, hafniumoxy-nitride, hafnium zirconium oxide and lanthanum oxide. In anotherembodiment, tunneling layer 242 is a multilayer tunneling layerincluding at least a bottom layer of a material such as, but not limitedto, silicon dioxide or silicon oxy-nitride and a top layer of a materialwhich may include, but is not limited to silicon nitride, aluminumoxide, hafnium oxide, zirconium oxide, hafnium silicate, zirconiumsilicate, hafnium oxy-nitride, hafnium zirconium oxide and lanthanumoxide.

Referring again to FIG. 2L, a charge-trapping layer 244 is formed on oroverlying the tunneling layer 242. Generally, as in the embodimentshown, the charge-trapping layer is a multilayer charge-trapping layerhaving multiple layers including at least an oxygen-rich, substantiallycharge trap free lower or first charge-trapping layer 244 a closer tothe tunneling layer 242, and an upper or second charge-trapping layer244 b that is silicon-rich and oxygen-lean relative to the firstcharge-trapping layer and comprises a majority of a charge trapsdistributed in multilayer charge-trapping layer.

The first charge-trapping layer 244 a of a multilayer charge-trappinglayer 244 can include a silicon nitride (Si₃N₄), silicon-rich siliconnitride or a silicon oxy-nitride (SiO_(x)N_(y) (H_(z))). For example,the first charge-trapping layer 244 a can include a silicon oxynitridelayer having a thickness of between about 1.5 nm and about 4.0 nm formedby a CVD process using dichlorosilane (DCS)/ammonia (NH₃) and nitrousoxide (N₂O)/NH₃ gas mixtures in ratios and at flow rates tailored toprovide a silicon-rich and oxygen-rich oxynitride layer.

The second charge-trapping layer 244 b of the multilayer charge-trappinglayer is then formed over the first charge-trapping layer 244 a. Thesecond charge-trapping layer 244 b can include a silicon nitride andsilicon oxy-nitride layer having a stoichiometric composition of oxygen,nitrogen and/or silicon different from that of the first charge-trappinglayer 244 a. The second charge-trapping layer 244 b can include asilicon oxynitride layer having a thickness of between about 2.0 nm andabout 10.0 nm, and may be formed or deposited by a CVD process using aprocess gas including DCS/NH₃ and N₂O/NH₃ gas mixtures in ratios and atflow rates tailored to provide a silicon-rich, oxygen-lean top nitridelayer.

As used herein, the terms “oxygen-rich” and “silicon-rich” are relativeto a stoichiometric silicon nitride, or “nitride,” commonly employed inthe art having a composition of (Si₃N₄) and with a refractive index (RI)of approximately 2.0. Thus, “oxygen-rich” silicon oxynitride entails ashift from stoichiometric silicon nitride toward a higher wt. % ofsilicon and oxygen (i.e. reduction of nitrogen). An oxygen rich siliconoxynitride film is therefore more like silicon dioxide and the RI isreduced toward the 1.45 RI of pure silicon dioxide. Similarly, filmsdescribed herein as “silicon-rich” entail a shift from stoichiometricsilicon nitride toward a higher wt. % of silicon with less oxygen thanan “oxygen-rich” film. A silicon-rich silicon oxynitride film istherefore more like silicon and the RI is increased toward the 3.5 RI ofpure silicon.

Referring again to FIG. 2L, the number of dielectric layers furtherincludes a blocking dielectric layer or blocking layer 246 that isformed on or overlying the charge-trapping layer 244. In one embodiment,the blocking layer 246 can include an oxidized portion of the siliconnitride of the underlying second charge-trapping layer 244 b, which issubsequently oxidized by in-situ-steam-generation (ISSG), or radicaloxidation to form the blocking layer 246. In other embodiments, theblocking layer 246 can include a silicon oxide (SiO₂) or a siliconoxynitride (SiON), deposited by CVD, and performed in a batch or singlesubstrate processing chamber with or without an ignition event such asplasma. The blocking layer 246 can be a single layer of silicon oxide,having a substantially homogeneous composition, a single layer ofsilicon oxynitride having a gradient in stoichiometric composition, or,as in embodiments described below, can be a multilayer blocking layerincluding at least a lower or first blocking layer overlying the secondcharge-trapping layer 244 b, and a second blocking layer overlying thefirst blocking layer.

In one embodiment, the blocking layer 246 can include a silicon nitride,a silicon-rich silicon nitride or a silicon-rich silicon oxynitridelayer having a thickness of between 2.0 nm and 4.0 nm formed by a CVDprocess using N₂O/NH₃ and DCS/NH₃ gas mixtures.

Referring to FIGS. 1 and 2M, a gate oxide or GOX preclean is performed,and gate oxides for MOS transistors 210 a-210 b formed (step 130).Referring to FIG. 2M, the GOX preclean removes the remaining pad oxides214 in the MOS regions 212 and at least a portion of the blocking layer246 in a highly selective cleaning process. This cleaning processprepares the substrate 204 in the MOS region 212 for gate oxide growth.In one exemplary implementation the pad oxide 214 is removed in a wetclean process. Alternatively, the wet clean process can be performedusing a 20:1 BOE wet etch, a 50:1 hydrofluoric (HF) wet etch, a padetch, or any other similar hydrofluoric-based wet etching chemistry. Inother embodiments, the cleaning process chemistry is chosen so as toremove only a negligible portion of the blocking layer 246.

In some embodiments, such as that shown in FIG. 2M, the oxidationprocess to form gate oxides for MOS transistors 210 a-210 b is a dualgate oxidation process to enable fabrication of both a first, thick,gate oxide 248 over the surface 216 of the substrate 204 in part of theMOS region 212 for a HV transistor, such as I/O MOSFET 210 b in the I/Ocircuit of the NVM, and a second, thinner gate oxide 250 for LVtransistors, such as core MOSFET 210 a. Generally, the dual gateoxidation process involves forming the thicker gate oxide 248 oversubstantially all of the MOS region 212, using any known oxidationprocess in accordance with the methods described herein, forming apatterned photoresist mask using standard lithographic techniquescovering the I/O MOSFET 210 b and NVM region 208, and removing the thickgate oxide covering core MOSFET 210 a by a wet etch process using a 10:1buffered oxide etch (BOE) containing a surfactant, after which thephotoresist mask is stripped or removed, and the second, thinner gateoxides 250 grown or deposited. The thinner gate oxides 250 can be grown,for example, to a thickness from about 1 nm to about 3 nm. It will beunderstood that, by controlling the thickness of the thick gate oxide248 as initially formed there is no need to form an additionalphotoresist mask over the I/O MOSFET 210 b during subsequent formationof the thinner gate oxide 250 since the additional oxide merely addsinsubstantially to the thickness of the thick gate oxide. Similarly, theoxidation process to form the thinner gate oxides 250 will have littleto no detrimental impact on the blocking layer 246.

In another embodiment, the oxidation process to form the thick gateoxide 248 is also used to concurrently form a high temperature oxide(HTO) over the dielectric stack 240 of the SONOS devices 206 to providea thicker oxide blocking layer 246 or an additional HTO layer of amultilayer blocking layer. The oxidation process can includein-situ-steam-generation (ISSG), CVD, or radical oxidation performed ina batch or single substrate processing chamber with or without anignition event such as plasma. For example, in one embodiment the thickgate oxide 248 and the additional or thicker oxide layer of the blockinglayer 246 may be grown in a radical oxidation process involving flowinghydrogen (H₂) and oxygen (O₂) gas into a processing chamber at a ratioto one another of approximately 1:1 without an ignition event, such asforming of a plasma, which would otherwise typically be used to pyrolyzethe H₂ and O₂ to form steam. Instead, the H₂ and O₂ are permitted toreact at a temperature approximately in the range of 800-1000° C. at apressure approximately in the range of 0.5-10 Torr to form radicals,such as, an OH radical, an HO₂ radical or an O diradical radicals at asurface of the blocking layer 246. The oxidation process is carried outfor a duration approximately in the range of 1-5 minutes for a singlesubstrate using an ISSG process, or 10-15 minutes for a batch furnaceprocess to effect growth of the blocking layer 246 having a thickness offrom about 2 nm to about 4.5 nm, and a thick gate oxide 248 having athickness of from about 3nm to about 7 nm.

Next, referring to FIGS. 1 and 2N-2O, a gate layer is deposited andpatterned to concurrently form a gates 252 for the MOS devices 210 a,210 b, and the SONOS devices 206 a, 206 b (step 132). Generally, thegate layer is a conductive, conformal layer deposited over substantiallythe entire surface 216 of the substrate 204 and all layers andstructures formed thereon. A patterned photoresist mask (not shown) isthen formed using standard lithographic techniques and the gate layeretched to remove the gate layer from areas not protected by the mask,stopping on top surfaces of the gate oxides 248, 250, and the dielectricstack (blocking layer 246) of the SONOS devices 206 a, 206 b.

In one embodiment, the gate layer includes a doped polysilicon or polylayer deposited using chemical vapor deposition (CVD) to a thickness offrom about 30 nm to about 100 nm, and etched using standard polysiliconetch chemistries, such as CHF₃ or C₂H₂ or HBr/O₂ which are highlyselective to the underlying material of the gate oxides 248, 250 and thedielectric stack 240. The polysilicon can be doped using phosphorusimplant for NMOS and Boron implant for PMOS transistors. The implantdoses are in the range of 1E15 to 1E16/cm² at energies of 2 to 50 KeV.

Referring to FIG. 2O, in some embodiments the gate layer is amulti-layer gate layer including one or more layers of a high workfunction or P+ metal, such as aluminum, Titanium or compounds or alloysthereof, in addition to or instead of polysilicon to form multi-layergates 252 including a first, high work function metal layer 252 a and asecond polysilicon layer 252 b.

Referring to FIGS. 1 and 2P a spacer layer is deposited and etched toform sidewall spacers 254 (spacer 1 ) adjacent to the gates 252 of theMOS and SONOS devices (step 134). The spacer layer can include aconformal layer of a dielectric material, such as silicon oxide (SiO2)or silicon nitride (SiN), deposited to a thickness of from about 10 nmto about 30 nm, using any known CVD technique as described herein. In anembodiment, where the spacer layer 254 includes silicon nitride, theetch may be accomplished or performed in a number of different waysincluding, for example, a low pressure blanket or spacer etch at amoderate power (about 500 W) in a plasma of a fluorine containing gas,such as CF₄, or CHF₃. Because no mask is used and the etching is highlyanisotropic, substantially all of the spacer layer is etched or removedfrom the exposed surface 216 of the substrate 204, as well as horizontalsurface of the gates 252, parallel to the surface of the substrateleaving spacers 254 adjacent to sidewalls of the gates of the of the MOSand SONOS devices.

Referring to FIG. 2P, it is noted that in embodiments in which thespacer layer includes an oxide, such as silicon-dioxide (SiO₂), any ofthe dielectric stack 240 as well as any of the GOX 248, 250, remainingon the surface 216 of the substrate 204 and not covered by the gates 252is advantageously removed along with portions of the spacer layerremoved to form the spacers 254.

Referring to FIGS. 1 and 2Q, a patterned mask (not shown) is formed andsource and drain (S/D) implants are performed to form source and drain(S/D) regions 256 for both the MOS devices 210 a,210 b, and the SONOSdevices 206 a,206 b (step 136). The patterned mask can include aphotoresist mask or a hardmask patterned to expose only the S/D regionsof the SONOS and MOS devices. It is noted that in FIG. 2Q and followingFIG. 2R only a portion of the substrate 204 including N-SONOS device 206b and core MOS device 210 a are shown in order to more clearly showdetails of the S/D implants and silicides formed in subsequent step. Itwill be understood that as described in the detailed description aboveand below, the above S/D implant step as well as the silicides stepbelow are performed on the P-SONOS device 206 a and I/O MOS device 210 bas well.

Referring to FIGS. 1, 2R and 2S, a silicide 258 is formed over thesurface 216 of the substrate 204 in all S/D regions and a localinterconnect and a metallization performed interconnecting some of thedevices (step 138). The silicide process may be any commonly employed inthe art, typically including a pre-clean etch, nickel metal deposition,anneal and wet strip. Advantageously, because the MOS devices 210 a, 210b, and the complementary pair of SONOS devices (P-SONOS 206 a andN-SONOS 206 b) are integrally formed on the same substrate 204, themetallization process can be used to form a first metal layer 260 a orlocal interconnect (LI) electrically coupling or connecting the drain ofthe N-SONOS device to the drain of the PSONOS device. Optionally, asshown in the sources of the P-SONOS device 206 a and N-SONOS device 206b may be further connected by a second metal layer 260 b or LI to one ofthe MOS devices 210 a,210 b, as shown in FIG. 2S, or connected to ohmiccontacts (not shown) formed in the substrate 204. The metallizationprocess may be any commonly employed in the art, typically including apre-clean etch, metal deposition by CVD or PECVD, anneal and wet strip.Suitable metals for the metallization process include titanium (Ti),tantalum (Ta), tungsten (W) and nitrides or alloys thereof In oneembodiment, the metal layers 260 a, 260 b, are tungsten (W) deposited byCVD over a titanium (Ti) seed layer, and a titanium-nitride (TiN)barrier layer.

Finally, the standard or baseline CMOS process flow is continued tosubstantially complete the front end fabrication a non-volatile memoryincluding a pair of complementary SONOS devices integrally formed with anumber of MOS devices, including at least one pair of CMOS devices.

An embodiment of another method for integrating or embedding CSONOS intoa CMOS process flow process flow will now be described in detail withreference to FIG. 3 and FIGS. 4A through 4J. FIG. 3 is a flowchartillustrating an embodiment of a method or process flow in which ahardmask is deposited over a surface of substrate after tunnel masks(TUNM) are formed for the CSONOS and SONOS wells and/or channelsimplanted. FIGS. 4A through 4J are block diagrams illustratingcross-sectional views of a portion of a memory cell 200, including apair of complementary SONOS devices and a number of MOS devices, two ofwhich are shown, during fabrication of the memory cell according to themethod of FIG. 3.

As with the hardmask-first method described above the process beginswith forming a number of isolation structures 202 in a wafer orsubstrate 204 and implanting dopants into substrate 204 through the padoxide 214 to form channels 218 and wells 220 for one or more of the MOSdevices 210 a-210 b. At this point the memory cell 200 is substantiallyidentical to that described above following steps 102 and 104, and shownin FIG. 2A.

Next, referring to FIGS. 3 and 4A, a first tunnel mask (TUNM 224) isformed by depositing a photoresist layer on or overlying substantiallyan entire surface 216 of the substrate 204, patterning the photoresistlayer using standard lithographic techniques (step 302). The depositionand patterning is accomplished in the same manner as that described inconnection with step 108 above. It is noted that the pad oxides 214isolates the surface 216 of the substrate 204 from the photoresist offirst TUNM 224 in all active regions of the SONOS and MOS devices206,210.

Referring again to FIG. 3 and FIG. 4A, dopants of an appropriate energyand concentration are implanted through the pad oxide 214 to form achannel 228 for the N-SONOS device 206 b, and, optionally, a well (notshown in this figure) in which the channel for the N-SONOS device isformed (step 304).

Referring to FIG. 3 and FIG. 4B, the first or N-TUNM 224 is removed orstripped in either an ashing process using oxygen plasma, or aphotoresist strip or solvent (step 306).

Next, referring to FIG. 3 and FIG. 4C, a second tunnel mask (TUNM 230)is formed by depositing a photoresist layer on or over substantially anentire surface of the surface 216 and patterned using standardlithographic techniques (step 308). Because an opening 232 in thepatterned photoresist layer exposes the P-SONOS region 208 a, the secondTUNM 230 may also be referred to as the P-TUNM.

Referring again to FIG. 3 and FIG. 4C, dopants of an appropriate energyand concentration are implanted through the pad oxide 214 to form achannel 234 and a well or deep well 236 in which the P-SONOS device 206a is formed (step 310).

Referring to FIG. 3 and FIG. 4D, the second or P-TUNM 230 is removed orstripped in either an ashing process using oxygen plasma, or aphotoresist strip or solvent (step 312).

Next, referring to FIG. 3 and FIG. 4E a hardmask 264 is deposited overthe surface 216 of the substrate 204 (step 314). The hardmask 264 isformed concurrently over both the P-SONOS region 208 a and the N-SONOSregion 208 b. In some embodiments, such as that shown, the hardmask 264is formed concurrently over substantially the entire surface 216 of thesubstrate 204, including both the P-SONOS region 208 a and the N-SONOSregion 208 b and the MOS region 212.

Generally, the hardmask 264, like the hardmask 222 described above, caninclude can one or more layers of material that can be patterned oropened using photoresist and standard lithographic techniques, but whichis not itself photosensitive and protects underlying surface andstructures formed therein from the photoresist and lithographicprocesses as well as from implants and etch process performed throughopenings formed in the hardmask. Suitable materials for the hardmask 264include, for example, a layer of from about 5 to about 20 nm of siliconnitride (Si_(x)N_(y)), or silicon oxynitride (SiON) deposited by anyknown nitride deposition process. For example, in one embodiment anitride hardmask is formed in step 314 in a low pressure chemical vapordeposition (LPCVD) process using a silicon source, such as silane(SiH₄), dichlorosilane (SiH₂Cl₂), tetrachlorosilane (SiCl₄) orBis-TertiaryButylAmino Silane (BTBAS), and a nitrogen source, such asNH₃ and N₂O.

Next, referring to FIG. 3 and FIG. 4F, a third tunnel mask (TUNM 266) isformed by depositing a photoresist layer on or over substantially anentire surface of the hardmask 264, and patterned using standardlithographic techniques (step 316). Because an opening 268 in thepatterned photoresist layer exposes a portion of the hardmask 264 inboth the P-SONOS region 208 a and the N-SONOS region 208 b the thirdTUNM 266 may also be referred to as a complementary tunnel mask orC-TUNM.

Referring to FIG. 3 and FIG. 4G, the portion of the hardmask 264 exposedthrough the opening 268 in the third or C-TUNM 266 is etched or removedusing any suitable wet or dry etching technique, depending on thematerial of the hardmask and the underlying structures or layers (step318). For example, as described above in connection with N-TUNM 224 andP-TUNM 230, in those embodiments in which the hardmask 264 includes alayer of silicon nitride overlying a pad oxide 214, the hardmask can beetched using a standard low pressure nitride etch at a moderate power(about 500 W) in a plasma of a fluorine containing gas, such as CF₄, orCHF₃, which exhibits good selectivity to silicon oxides, such as thesilicon dioxide (SiO2) of the underlying pad oxide 214 and/or the STI202 structures.

Referring to FIG. 3 and FIG. 4H, the second or C-TUNM 266 is removed orstripped in either an ashing process using oxygen plasma, or aphotoresist strip or solvent (step 320).

Next, referring to FIG. 3 and FIG. 41, the pad oxide 214 over both theP-SONOS region 208 a and the N-SONOS region 208 b is concurrentlyremoved in a tunnel mask etch through the opening formed in the hardmask466 (step 322). The tunnel mask etch can be accomplished, for example,in a wet clean process using a 10:1 buffered oxide etch (BOE) containinga surfactant. Alternatively, the wet clean process can be performedusing a 20:1 BOE wet etch, a 50:1 hydrofluoric (HF) wet etch, a padetch, or any other similar hydrofluoric-based wet etching chemistry.

Finally, referring to FIG. 3 and FIG. 4J, the hardmask 264 issubstantially entirely stripped or removed (step 324). The hardmask 264can be removed using the same process and chemistry previously used toform openings in the hardmask. For example, in embodiments in which thehardmask 264 includes a silicon nitride layer, it can be removed using astandard low pressure nitride etch at a moderate power (about 500 W) ina plasma of a fluorine containing gas, such as CF₄, or CHF₃, whichexhibits good selectivity to silicon oxides, such as the silicon dioxide(SiO2) of the pad oxide 214 remaining over the MOS devices 210 a-210 bin the MOS region 212 and the STI 202 structures, and to the underlyingsilicon of the substrate in the SONOS region 208. The silicon nitridecan also be removed by a wet etch using Phosphoric acid (H₃PO₄) at atemperature of about 150° C. to 160 C.

The method then continues as provided in steps 128 through 138 asdescribed above, and a standard or baseline CMOS process flow isperformed to substantially complete the front end fabrication of anon-volatile memory including a pair of complementary SONOS devicesintegrally formed with a number of MOS devices, including at least onepair of CMOS devices.

In an alternative embodiment of either of the methods shown in FIGS. 1and 3, prior to depositing the hardmask 222/264 a well or wells areconcurrently implanted for at least one of the number of MOS devices inthe MOS region and a well for one of the pair of complementary SONOSdevices in the P-SONOS region or the N-SONOS region. FIG. 5 is a blockdiagram illustrating cross-sectional views of a portion of a memory cellfabricated to include a deep Nwell 270 concurrently formed in theP-SONOS region 208 a and the MOS region 212 in which the core MOS 210 ais subsequently formed. As noted above, the deep Nwell 270 can beimplanted with Arsenic or Phosphorous at an energy of from about 500 toabout 2000 kilo-electron volts (keV), and a dose of from about 5E12/cm²to about 2E13/cm² to form a deep Nwell. Furthermore, although theP-SONOS region 208 a is shown as having been relocated to be adjacent tothe MOS region 212 in which the core MOS 210 a is formed and the deepNwell 270 is shown as being one contiguous well, it will be understoodthat this need not be the case in every embodiment, and the wells canconcurrently be formed while remaining separate or non-contiguous byappropriate patterning of an implant mask.

Thus, embodiments of methods for fabricating memory cells includingembedded or integrally pair of complementary SONOS devices and a numberof MOS devices have been described. Although the present disclosure hasbeen described with reference to specific exemplary embodiments, it willbe evident that various modifications and changes may be made to theseembodiments without departing from the broader spirit and scope of thedisclosure. Accordingly, the specification and drawings are to beregarded in an illustrative rather than a restrictive sense.

The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b), requiring an abstract that will allow the reader to quicklyascertain the nature of one or more embodiments of the technicaldisclosure. It is submitted with the understanding that it will not beused to interpret or limit the scope or meaning of the claims. Inaddition, in the foregoing Detailed Description, it can be seen thatvarious features are grouped together in a single embodiment for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted as reflecting an intention that the claimedembodiments require more features than are expressly recited in eachclaim. Rather, as the following claims reflect, inventive subject matterlies in less than all features of a single disclosed embodiment. Thus,the following claims are hereby incorporated into the DetailedDescription, with each claim standing on its own as a separateembodiment.

Reference in the description to one embodiment or an embodiment meansthat a particular feature, structure, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe circuit or method. The appearances of the phrase one embodiment invarious places in the specification do not necessarily all refer to thesame embodiment.

What is claimed is:
 1. A method comprising: implanting a channel for anNSONOS device through a first pad oxide overlying an N-SONOS region of asubstrate; implanting a channel for a PSONOS device through a second padoxide overlying a P-SONOS region of the substrate; and concurrentlyimplanting a number of Nwells for the PSONOS device and a PMOS device ina MOS region of the substrate, wherein the PMOS device is a low voltage(LV) PMOS device, and wherein concurrently implanting a number of Nwellsfor the PSONOS device and the PMOS device comprises implanting a single,contiguous deep Nwell for the PSONOS device and the PMOS device.
 2. Themethod of claim 1 further comprising, prior to implanting the channelfor the NSONOS device, forming trench isolation structures including afirst trench isolation structure that isolates a source/drain (S/D)region of the PMOS device from a first S/D region of the PSONOS deviceat the surface of the substrate, wherein the first trench isolationstructure does not extend through a full depth of the single, contiguousdeep Nwell for the PSONOS device and the PMOS device.
 3. The method ofclaim 2 further comprising depositing and patterning a metal layer overthe surface of the substrate and the trench isolation structures to forma first local interconnect (LI) connecting the S/D region of the PMOSdevice and the first S/D region of the PSONOS device.
 4. The method ofclaim 3 wherein forming trench isolation structures further comprisesforming a second trench isolation structure that isolates a second S/Dregion of the PSONOS device from an S/D region of the NSONOS device. 5.The method of claim 4 wherein depositing and patterning the metal layerfurther comprises concurrently forming a second LI, co-planar with thefirst LI, and connecting the second S/D region of the PSONOS device withthe S/D region of the NSONOS device.
 6. The method of claim 1 wherein:implanting the channel for the NSONOS device comprises depositing andpatterning a first photoresist mask over a surface of the substrate toexpose the N-SONOS region, implanting the channel for the NSONOS devicethrough the first pad oxide and removing the first photoresist mask; andimplanting the channel for the PSONOS device comprises depositing andpatterning a second photoresist mask over the surface of the substrateto expose the P-SONOS region, implanting the channel for the PSONOSdevice through the second pad oxide and removing the second photoresistmask, wherein the second pad oxide separates the first photoresist maskfrom the P-SONOS region, and the first pad oxide separates the secondphotoresist mask from the N-SONOS region.
 7. The method of claim 6further comprising: depositing and patterning a hardmask (HM) over theN-SONOS region and the P-SONOS region to expose the N-SONOS region andthe P-SONOS region; and concurrently removing the first and second padoxides in the N-SONOS region and the P-SONOS region.
 8. The method ofclaim 7 further comprising: removing the HM; depositing a number ofdielectric layers over the surface of the substrate, the dielectriclayers include a tunneling layer overlying the surface of the substrate,a charge-trapping layer overlying the tunneling layer and a blockinglayer overlying the charge-trapping layer; and etching the number ofdielectric layers to form dielectric stacks for the NSONOS device andPSONOS device.
 9. A method comprising: depositing and patterning a firstphotoresist mask over a surface of a substrate to expose an N-SONOSregion, implanting a channel for an NSONOS device through a first padoxide overlying an N-SONOS region of the substrate; depositing andpatterning a second photoresist mask over the surface of the substrateto expose a P-SONOS region, implanting a channel for a PSONOS devicethrough a second pad oxide and removing the second photoresist mask; andconcurrently implanting a number of Nwells for the PSONOS device and aPMOS device in a core region of the substrate; concurrently removing thefirst and second pad oxides in the N-SONOS region and the P-SONOSregion; and forming a high-voltage MOS device in an input-output (I/O)region of the substrate separated from the P-SONOS region by the coreregion, wherein the second pad oxide separates the first photoresistmask from the P-SONOS region, and the first pad oxide separates thesecond photoresist mask from the N-SONOS region, wherein the PMOS deviceis a low voltage (LV) PMOS device, and wherein concurrently implanting anumber of Nwells for the PSONOS device and the PMOS device comprisesimplanting a single, contiguous deep Nwell for the PSONOS device and thePMOS device.
 10. The method of claim 9 further comprising, prior toimplanting the channel for the NSONOS device: forming trench isolationstructures including a first trench isolation structure that isolates asource/drain (S/D) region of the PMOS device from a first S/D region ofthe PSONOS device at the surface of the substrate, wherein the firsttrench isolation structure does not extend through a full depth of thesingle, contiguous deep Nwell for the PSONOS device and the PMOS device;and depositing and patterning a metal layer over the surface of thesubstrate and the trench isolation structures to form a first localinterconnect (LI) connecting the S/D region of the PMOS device and thefirst S/D region of the PSONOS device.
 11. The method of claim 10wherein forming trench isolation structures further comprises forming asecond trench isolation structure that isolates a second S/D region ofthe PSONOS device from a S/D region of the NSONOS device, and whereindepositing and patterning the metal layer further comprises concurrentlyforming a second LI, co-planar with the first LI, and connecting thesecond S/D region of the PSONOS device with the S/D region of the NSONOSdevice.
 12. The method of claim 9 further comprising: depositing anumber of dielectric layers over the surface of the substrate, thedielectric layers include a tunneling layer overlying the surface of thesubstrate, a charge-trapping layer overlying the tunneling layer and ablocking layer overlying the charge-trapping layer; and etching thenumber of dielectric layers to form dielectric stacks for the NSONOSdevice and PSONOS device.
 13. A method comprising: implanting acontiguous deep well in which at least one low voltage (LV) MOS devicein a MOS region of a substrate and one SONOS device of a pair ofcomplementary SONOS devices in a P-SONOS region or an N-SONOS region ofthe substrate are formed; depositing and patterning a first photoresistmask over a surface of the substrate to expose the N-SONOS region,implanting a channel for an N-type SONOS device through a first padoxide overlying the N-SONOS region and removing the first photoresistmask; depositing and patterning a second photoresist mask over thesurface of the substrate to expose the P-SONOS region, implanting achannel for a P-type SONOS device through a second pad oxide overlyingthe P-SONOS region and removing the second photoresist mask; anddepositing and patterning a hardmask (HM) over the N-SONOS region andthe P-SONOS region to expose the N-SONOS region and the P-SONOS region;and concurrently removing the first and second pad oxides in the N-SONOSregion and the P-SONOS region, wherein the second pad oxide separatesthe first photoresist mask from the P-SONOS region, and the first padoxide separates the second photoresist mask from the N-SONOS region. 14.The method of claim 13 further comprising, prior to implanting thecontiguous deep well, forming trench isolation structures including afirst trench isolation structure that does not extend through a fulldepth of the contiguous deep well and isolates a source/drain (S/D)region of the at least one LV MOS device from a first S/D region of theone SONOS device at the surface of the substrate.
 15. The method ofclaim 14 further comprising depositing and patterning a metal layer overthe surface of the substrate and the trench isolation structures to forma first local interconnect (LI) connecting the S/D region of the atleast one LV MOS device and the first S/D region of the one SONOSdevice.
 16. The method of claim 15 wherein forming trench isolationstructures further includes forming a second trench isolation structurethat isolates a second S/D region of the one SONOS device from a S/Dregion of the other SONOS device of the pair of complementary SONOSdevices, and wherein depositing and patterning the metal layer furthercomprises concurrently forming a second LI, co-planar with the first LI,and connecting the second S/D region of the one SONOS device with theS/D region of the other SONOS device of the pair of complementary SONOSdevices.
 17. The method of claim 13 further comprising: removing the HM;depositing a number of dielectric layers over the surface of thesubstrate, the dielectric layers include a tunneling layer overlying thesurface of the substrate, a charge-trapping layer overlying thetunneling layer and a blocking layer overlying the charge-trappinglayer; and etching the number of dielectric layers to form dielectricstacks for the pair of complementary SONOS devices.